I just realised that Raghu has been choosing invention related movies. He loves:
Charlie and Chocolate Factory... specifically listens and talks about Mr. Wonka (He is yet to see the new one)
Robots a fab movie about a young Robot inventor.
Meet the Robinsons about a young orphaned child who dreams of building a time machine to go back in time and find his mom.
And Raghu says a null-void-protector is the invention aspect of the Ben10 movie he saw recently.
He has watched these movies over and over... and talks to me often about building games, inventing things that will make it possible for us to fly etc. What fun to talk about stuff with him and see his intense curiosity, love for inventions etc... grow.